The machining of objects by means of coherent radiation, especially laser radiation, is a well known technique. However, many industrial applications require levels of quality and reproducibility which cannot be met with known laser beam techniques. In general, the machining shows disturbing phenomena, e.g., thermal destruction of surrounding material, deposition around the machined area of material ejected in liquid state, and poorly defined boundaries of the machined area. The machining of a large number (.perspectiveto.10.sup.8) of holes of precisely controlled size, e.g., equal within volume variations of less than 1%, or of controlled different sizes, e.g., 100 discrete volume steps, has not heretofore been accomplished with laser radiation.
Systematic investigations of the events during laser heating and vaporization of transparent media and highly reflective metals have led recently to a new machining technique by which the disturbing phenomena could be avoided. This machining technique disclosed in copending U.S. patent application Ser. No. 728,403 is based on laser systems characterized by fundamental mode operation which affords constant energy output, with controlled emission time. This emission can be adapted to the kind of machining and to the material machined to achieve optimum quality. To machine a number of small discrete areas distributed on an object one can either (1) move the object continuously and chop the radiation (short pulses), or (2) move the object in a stop-and-go manner and use longer pulses, or (3) move the object and direct the radiation to machine successive areas spaced on the object along the direction of movement. In the first case (1), the duration of one radiation pulse must be adapted to the speed of movement and to the dimension of the machined area. The second case (2), in which the object is moved in a stop-and-go manner, needs stepping motors capable of accelerating and decelerating the object. This clearly limits the applicability of this method to small, light objects. Directing the beam (3) over the entire number of areas can only be accomplished at the requisite high beam powers with present techniques if the space occupied by the areas is confined within narrow limits, the practical extent of which depends on the necessary access time.